Optical temperature detection devices measure the light radiated by objects to determine the temperature of the objects, without contacting the object. Such devices have great flexibility and can be utilized in various applications, including but not limited to, measuring critical temperatures during glass and plastic manufacturing processes. Depending on the application, optical temperature detection devices can also be manufactured with different operating parameters, such as portability, range, accuracy and size.
Optical temperature detection devices have several advantages over other temperature detection devices that contact the object, including such advantages as, the response time being vastly improved, and eliminating the need to make good contact with the object. Unfortunately, along with the above named benefits, come several disadvantages, including, but not limited to, inaccurate readings due to contamination of the optical lens or window. The contamination of the optical lens or window prevents the optical sensor from having a needed unobstructed line of sight to the object, hence preventing the optical sensor from properly reading the temperature of the object.
The contamination of the optical lens or window can occur in many ways. Most obvious and easiest to prevent is the actual touching and scraping of the lens or window with foreign objects such as fingers and tools. Less obvious and more difficult to prevent is the deposit of contaminants on the lens or window, placed there by the surrounding ambient air.
There have been several attempts made in the art to prevent the deposit of contaminants on the lens or window, including purging the area proximate to the lens or window with forced gas. More specifically, the purging process has been accomplished by placing a hollow housing over the area exposed to the lens and forcing through an outlet at the base of the housing near the lens, an air stream that creates a contaminant free area in front of the lens by forcing all of the ambient air away from the lens. Although somewhat effective, the application of this purging process is limited to optical sensors with narrow field of views.
Similar attempts to rid the lens of contaminants have been made by directing a small stream of gas directly toward the lens. This process and apparatus, even though useable on a great variety of lenses and taking up relatively little space, is limited in effectiveness in that the generated stream of gas has a tendency to commingle with ambient air as it approaches the lens, thereby allowing the lens to once again become contaminated with ambient air particles.
To overcome the problems of commingling air, others in the art have attempted to create a contaminant free area in front of the lens by forcing a laminar gas flow past the lens. Even though forcing a laminar gas flow past the lens has been effective, other important variables had to be sacrificed. For example, due to the large area needed for housing the length of conduit necessary to produce such a laminar gas flow, the footprints of such devices become so large as to be unusable in many applications.